Invention relates to ink jet printer apparatus and systems, and in particular is directed to a method for fabricating an ink jet nozzle structure or print head to achieve a desired geometry and consistency in production.
In ink jet printers, generally an ink jet nozzle structure or print head is formed on a small "chip" of rigid material constructed to have an ink inlet, an ink chamber and an ink jet nozzle for each plurality of streams or jets of ink to be expelled toward a surface upon which printing is to be executed. The ink jets may comprise a continuously pumped stream which is electrostatically charged and steered by a variable electric field; or they can be in a series or matrix of jet nozzles, each of which expels a drop of ink at a time on demand. These "drop on demand" ink jet printers are often controlled by pulses of pressure on a bladder-like ink chamber just upstream of the nozzle, with each pulse producing a single droplet of ink. The ink chamber is continuously resupplied with ink from an inlet end to replenish ink expelled in the series of droplets. Drop on demand ink jet nozzles may be pulsed by piezoelectric pulsing of the bladder or by heating of a region inside the ink chamber, sometimes known as "bubble jet."
Patents showing conventional ink jet print heads include U.S. Pat. Nos. 3,946,398, 4,189,734, 4,216,483, 4,339,763, 4,125,845 and 4,506,276.
In the fabrication of print heads or nozzle heads for ink jet printers, it has been conventional to use a base piece of photoform glass, which is exposed photographically in the pattern (in plan view) of ink channels which is desired and then developed, then subjected to an acid etch on one side to form the channels. The channels generally are to be of different depths in different portions of their lengths, with a deeper portion for the ink chamber. The different depths have conventionally been achieved using a double etching procedure. In one step of the double etching process, the shallower portions of the channel are masked off by tape or other masking agents. Thus, the masked off areas are not etched while masked, but are only etched in another step wherein the photoform glass base is unmasked. As a result, the areas which have been masked part of the time are etched to a lesser depth than the ink chamber portion, which is not masked at all during etching.
Taping, which has usually been used for the masking of the shallower portions in one phase of the acid etching of the photoform glass plate, has been inherently subject to error and variation in the positioning of the tape and in the resulting etched product. It has been difficult to consistently place the tape in precisely the correct position transversely across the channels; also, even with tape correctly positioned, the acid will under-etch the tape to some degree and to a varying degree from plate to plate, resulting in a nonsharp transition and variation in the geometry of the print head from part to part in the manufacturing process. This results in variation in the printing performance from print head to print head, and is thus very undesirable.
It is desirable to have transitions between the shallow and deep areas of print head channels which are extremely consistent in location from print head to print head, which are sharp and square in cross section, and which exhibit precise uniformity in performance characteristics in service of the print heads. These are objects of the present invention described below.